1. Field of the Invention
The present invention relates to magnetic material and particularly to a magnetic amorphous alloy sheet. More particularly, the present invention relates to a magnetic amorphous alloy sheet on which a film is applied so as to minimize deterioration of the magnetic properties thereof when blanked sections of the mangetic amorphous alloy sheet are laminated or when the magnetic amorphous alloy sheet is wound.
The core of electrical machinery and apparatuses, for example, a transformer, must be comprised of magnetic material, the fundamental properties of the material being a high saturation flux density, a low watt loss, and a high permeability. The core material must exhibit these fundamental properties when it is shaped or worked so that it has a toroidal form or a laminated form. The watt loss and permeability are, however, liable to be influenced by the working of or shaping of a magnetic material sheet. The watt loss and permeability usually deteriorate when stress is induced in a magnetic material sheet due to the working or shaping thereof. The ratio of a magnetic property of a core to a magnetic property of a magnetic material sheet is referred to as the building factor.
Usually, the watt loss is the magnetic property used for determining the building factor. A small building factor, that is, a building factor close to 1.00, indicates a more preferred magnetic property in the light of practical application of the magnetic material.
With regard to a grain-oriented electrical sheet, when a wound core is formed from a grain-oriented electrical steel sheet, the building factor ranges from 1.1 to 1.3.
2. Description of the Prior Art
An amorphous alloy is a metal alloy, the atomic arrangement of which is a random arrangement such as that in liquid form. An amorphous alloy can be produced by dropping on a cooled substrate molten metal containing a vitrification element and supercooling the molten metal. The composition of an amorphous alloy having good magnetic properties is one consisting of one or more of Fe, Co, and Ni in a total amount of from 70 atomic % to 88 atomic %, B in an amount of from 7 atomic % to 25 atomic %, and one or more of Si, P, and C in an amount balancing the above-mentioned Fe, Co, Ni, and B. One or more of Cr, Mo, Nb, and V may occasionally be added to the composition in an amount of up to 5 atomic %.
Since an amorphous alloy can be easily produced by the method described hereinabove and since it has many superior properties as compared with a crystalline alloy, it has attracted attention as an alloy which can be used for practical purposes. Especially, an amorphous alloy has a number of superior magnetic properties as compared with conventional magnetic materials, that is, the watt loss of an amorphous alloy is approximately one tenth or less lower than that of a grain-oriented electrical steel sheet, the permeability is higher than that of Permalloy, e.g., Ni--20%.about.25% Fe alloy, and the magnetic flux density is higher than that of ferrite. Thus, an amorphous alloy is most practically applied in the field of magnetic materials.
The term "magnetic amorphous alloy" herein means an amorphous alloy having a good watt loss, permeability, and/or magnetic flux density which enable it to be used in electrical machinery and devices, such as a transformer, and particularly means an amorphous magnetic alloy having the composition given hereinabove.
When a magnetic amorphous alloy is used as the core of a transformer, it is usually used as a wound core in which a magnetic amorphous alloy sheet is wound in a toroidal form or as a laminated core in which sections or pieces of a magnetic amorphous alloy sheet are laminated.
A magnetic amorphous alloy generally has a high building factor. For example, when a wound core having an inner diameter of 40 mm is formed by winding a magnetic amorphous alloy core, the building factor ranges from 1.5 to 2.0. A magnetic amorphous alloy has strain-sensitive magnetic properties and cannot be subjected to high-temperature stress relief annealing so as to satisfactorily remove the stress, stress relief annealing usually being carried out at a temperature from 360.degree. C. to 380.degree. C. for a time period of from 30 to 60 minutes. A magnetic amorphous alloy does not crystallize at a temperature from 360.degree. C. to 380.degree. C., but stress relief annealing at this temperature is unsatisfactory for relieving the stress. Therefore, due to the strain-sensitive magnetic properties, which do not allow a magnetic amorphous alloy to be subjected to high-temperature stress relief annealing, the building factor thereof is low.
As is known, the building factor is influenced by the layer insulation resistance of a core. That is, the building factor increases by increase in the eddy current which flows across a layer when the layer insulation resistance of a core is low. In order to provide a low-building-factor core comprising a grain-oriented electrical steel or Permalloy sheet, an insulating film is applied on the sheet.
Since a magnetic amorphous alloy has a resistivity a few times higher than that of crystalline magnetic materials, such as a grain-oriented electrical steel and Permalloy, the eddy current induced in the magnetic amorphous alloy is inherently small. In addition, since magnetic amorphous alloy sheets have appropriate unevennesses which prevent face contacts therebetween, the layer insulation resistance is high. Therefore, it is believed by persons skilled in the art that it is not necessary to increase the layer insulation resistance by applying an insulating film on a magnetic amorphous alloy sheet.
As is known, the building factor is enhanced when rust forms on a magnetic material sheet since the magnetic properties thereof are thereby impaired and since the magnetic material sheet becomes locally thick in the regions of rust formation. Conventional magnetic alloy material is not so good corrosion-resistant and therefore does not effectively prevent the formation of rust.